Differential recovery of adrenocortical responses to neural stimuli following administration of 5,7-dihydroxytryptamine into the hypothalamus

Summary In view of the role of serotonin in adrenocortical regulation, the effects of depletion of hypothalamic serotonin, using localized injections of the neurotoxin 5,7-dihydroxytryptamine into the hypothalamic paraventricular nucleus, on the rise in plasma corticosterone following afferent neural stimulation, were studied. The neurotoxin caused a significant reduction (p<0.001) in hypothalamic serotonin content of about 50% during the first month and about 30% up to two months later. Basal and ether stress-induced rises in plasma corticosterone levels were unaffected at all times after this treatment, but responses to stimulation of the sciatic nerve were reduced for up to four weeks (p<0.01), recovering at later times. Responses to photic and acoustic stimuli were almost entirely prevented up to four weeks following the treatment (p<0.001) but showed a gradual recovery to full, or almost full, adrenocortical responses at eight weeks, following acoustic and photic stimulation respectively. These results demonstrate a differential recovery of the adrenocortical responses, following the neurotoxin injection and indicate that different neural modalities require different 5-HT concentrations in the PVN for the expression of a full adrenocortical response.